Automatic variable pitch propeller



R. L. KELM AUTOMATIC VARIABLE PITCH PROPELLER April 3, 1934 Filed Nov. 8, 1932 IIJENTQR Mia 7 Patented Apr. 3, 1934 UNITED STATES PATENT OFFICE 1,953,682 AUTOMATIc VARIABLE rr'ron PROPELLER Robert L. Kehn, Lake View, N. Y. Application November 8, 1032, Serial No. 641,725 3 Claims. (Cl. 170-162) This invention relates to an automatically represents the rotatable member of the motor variable pitch propeller which is more particuwhich is adapted to drive the propeller, such for larly intended for use in propelling aeroplanes. example as the horizontal crank or driving shaft As is wellknown to operators of aeroplanes conof the gas engine of a kind now commonly em- 6 siderably more power is required to lift the aeroployed for propelling aeroplanes. 65 plane from the ground than is required for pro- Upon the end of this driving or power shaft pelling the same through the air after the same is mounted the variable pitch propeller which has been elevated. For example, an engine after embodies myinvention and which in its prestarting from a standstill may run 2400 revoluferred form is constructed as follows:

tions per minute by the time the aeroplane is The numeral 11 represents a hub preferably 70 lifted but when in the air 1600 revolutions per of cylindrical form secured to the end of the minute will sufiice to continue its propulsion asdriving shaft by means of a key 12, as shown suming that the pitch of the propeller is fixed. in Figs. 1, 2 and 51, or by any other suitable It is also well-known that a propeller having means.

its blade arranged at a small pitch exerts a From this hub a. plurality of guide tubes 13 75 more powerful grip on the air than one having extend radially, two of such tubes being shown its blades pitch ata relatively great angle. in Figs. 1 and 2 arranged on diametrically oppo- This invention proposes utilizing this action site sides of the hub. Adjacent to the outer ends advantageously by providing a propeller having of these guide tubes are arranged propeller blades capable of being adjusted as to their pitch blades 14 which may be of any suitable con- 80' or angularity relative to the plane of rotation struction and trend in opposite directions, so and automatically actuating said blades so that far as the angularity of their front faces or the same when standing still or rotating at low working surfaces are concerned, in a manner speed will be arranged at a relatively great pitch common to propeller blades of tliis type.

or angle, but when running at high speed will Each of these propeller blades is provided at be arranged at a small pitch or angle. As a reits inner end with a cylindrical shank 15 which is sult the aeroplane can be lifted very easily and arranged concentrically within the adjacent quickly from the ground by running the engine guide tube and is capable of both a longitudinal at a high speed while the propeller blades are and also a. rotary motion relative to said tube.

30 at a small pitch, and when the aeroplane is off At its inner end each shank 15 is provided with the ground the speed ofthe engine can be rea supporting collar 16 preferably of circular form, duced to avoid unnecessary wear and expendiwhich collar is preferably rigidly secured to the ture of power but still propel the aeroplane with respective shank so as to be compelled to move ease while the blades assume a position of greatlengthwise and also rotate therewith. The pre- 5 er angularity or pitch. ferred means for accomplishing this consists of It is the purpose of this invention to provide a a square or fiat sided neck 17 arranged at the propeller which is capable of performing this inner end of the shank 15 and engaging with a function by simple, efficient and reliable means correspondingly shaped opening 18 in the center which operate to automatically turn the blades of the collar 16, and a screw nut 19 engaging with 40 y C fugal forc from One Of high a ularity the inner side of the supporting collar 16 and or pitch to one of low angularity or pitch as the mounted on a screw threaded stem 20 which prospeed of the engine increases, and to return the jects inwardly from the respective neck 17. Unblad y pr n mean f m a p i i n f 1 w screwing of this nut due to vibration of the propi h or an ularity as the speed of the en ine peller is prevented by providing this nut with 45 is r du d, th r y s urin unif mity f a ti n a plurality of radial notches 21 so that the same and reducing the cost of maintenance. is of castellated form and engaging a pair of In the accompanying drawing: diametrically opposite notches by means of a Figure 1 is a front elevation, on a reduced cotter pin 22 extending through the adjacent scale, of an aeroplane propeller embodying my part of the stem 20,,as shown in Fig. 2.

- invention and showing the parts in the position The inner end ofeach shank is guided in the which they occupy when the propeller is at rest. bore of the respective guide tube so as to be Figure 2 is a fragmentary longitudinal section capable of reciprocating lengthwise therein and of the propeller on an enlarged scale. also rotating about the axis of the shank and Figures 3 and 4 are transverse sections of the tube, this being accomplished in the present in- 55 same taken on the correspondingly numbered stance by means of a ball bearing comprising an lines in Fig. 2. inner bearing ring 23, an outer bearing ring 24,

In the following description similar characters and an annular row of balls 25 interposed beof reference indicate like parts in the several tween ball races 26, 27 formed on the opposing figures of the drawing. sides of the bearing rings 23 and 24,- as shown in 60 Referring to the drawing, the numeral 10 Fig. 2, Each of these bearing rings engages its 1 0 bore and periphery with the outer side of the shank 15 and the inner side of the guide tube, and the inner ring additionally engages its rear lateral side with the front side of the supporting collar 16.

During the operation of this propeller this ball bearing unit moves lengthwise with the shank in the guide tube which is radial with reference to the axis of rotation of the driving shaft 10, and these bearing rings are also free to rotate one relatively to the other about the axis of the shank and guide tube, the friction of which movement is reduced to a minimum due to the presence of the balls 25 between these bearing rings, thereby enabling these movements to be effected easily and without undue wear.

The outer part of the shank of each blade is mounted on the outer part of the respective guide tube by means of a bearing which permits the shank to rotate and also slide relative to the adjacent part of the guide tube, which bearing comprises inner and outer bearing. rings 28, 29, and an annular row of balls 30 interposed between the ball races 31, 32 which are formed on the opposing surfaces of these bearing rings. The inner bearing ring 28 engages with the periphery of the shank 15 and the outer bearing ring 29 bears with its periphery against the bore 33 of an outer supporting ring 34, while the rear side of this last-mentioned bearing ring engages with an outwardly facing shoulder 35 on this supporting ring.

The periphery of this last-mentioned supporting ring engages with a bore 36 of a cylindrical enlargement at the outer end of the respective guide tube, and the rear side of this supporting ring engages with an outwardly or forwardly fac ing shoulder 37 at the inner end of the enlarged bore 36, as shown in Fig. 2.

The outer supporting ring 34 is held in place on the respective guide tube and the two bearin rings 28 and 29 of the front ball bearing are held in place within the outer supporting ring 34 by a screw cap, the crown 38 of which engages the front ends of the bearing rings 28, 29 while the flange 39 thereof is connected by means of a screw joint 40 with the outer end of the respective guide tube, as shown in Fig. 2.

The shank 15 of each propeller blade is yieldingly held in its innermost position radially by means of a return spring 41 which surrounds the shank within the guide tube and bears at its inner end against the front ring 24 of the rear ball bearing, while the outer end of this spring bears against the inner side of the outer supporting ring 34 for the purpose, of causing the rotary sliding movement of the shank and the parts associated therewith to.be efiected without binding, the interior of the guide tube is filled with a lubricant and escape of the latter from the guide tube is prevented by means of a circular packing 42 surrounding the outer part of the shank and'seated in an annular groove 43 of a flange 44 on the outer side of the crown 38 of the retaining cap.

Means are provided whereby, upon moving the shank blade and associated parts radially outward relative to the axis of the driving shaft, this blade will be automatically turned by centrifugal force so that it will be shifted from a position in which the blade is arranged at a great angle relative to the plane of rotation into a position in which the blade assumes a small angularity or pitch relatively to this plane, and when the propeller ceases to rotate each propeller blade will be turned back from a position of small angularity to one of great angularity relative to the plane of rotation.

The means for this purpose preferably consist of a shifting pin 45 secured to the periphery of the supporting collar 16 and engaging with a helical or cam slot 46 formed in the adjacent part of the guide tube, as shown in Figs. 1 and 3.

The cap at the outer end of each guide tube is prevented from unscrewing due to vibration of the propeller by means of a nut lock which preferably consists of a ring 4'7 engaging with the inner end of the flange of each cap and provided with a plurality of prongs 48 engaging with an annular external groove 49 and flat faces 52 on the periphery of the flange of this can, and an inner prong 50 which is bent into a notch 51 on the adjacent screw threaded part of the guide tube after the cap has been tightened on the respective guide tube. By thus preventing the cap from unscrewing, the several parts constituting the means for mounting each blade on the respective guide tube are reliably held in their assembled position and thus insure proper operation of the propeller at all times.

When the propeller of the aeroplane is at rest the shanks of the blades are in their innermost radial positions within the guide tubes, and the shanks and blades are turned about their radial axes through the medium of the helical or cam slots 46 operating upon the shifting pins 45 so that the blades are arranged at the greatest angularity or angle of incidence relative to the plane of rotation of the blades. The blades, shanks and associated parts moving therewith are yieldingly retained in this position by the springs 41, and the extent of the inward movement of these shanks and the backward rotation of the blades is limited by engagement of the shifting pins with the rear ends of the helical or cam slots 46, as shown in Fig. 1.

Upon starting the rotation of the propeller while the parts are in this position a maximum of air resistance is encountered by the blades inasmuch as the angle of incidence of the blades at this time is the highest.

As the speed of the propeller increases, the centrifugal force exerted upon the blades due to this speed causes the blades, shanks and associated parts to be thrown radially outward and the springs 41 to be compressed. At the same time the shifting pins 45 acting upon the helical or cam slots 46 during this outward movement of the shanks and blades, will cause the shanks and blades to be turned about their radial axes so that when these pins reach the outer ends of these slots the blades have been turned about their radial axes into a position in which they present the lowest pitch or angle of incidence of their front or advancing surfaces to the plane of rotation, and thereby correspondingly increase the grip of the blades on the air and the propelling effect of the same.

In practice the engine is run at-high speed and with the blades of the propeller at their greatest pitch or angularity only during the time the plane is being lifted from the ground and then the speed of the engine is reduced to normal running, and when this occurs the reduction in the centrifugal force on the blades permits the springs 41 to draw the blade radially inwardly, and the shifting pins 45 and cam slots 46 to turn the blades into a position in which the pitch or angularity of the same is increased to the maximum, whereby the plane is propelled in the air at an increased speed while the engine is running at a reduced speed.

By this means the motor may be operated at a high initial speed with the blades of the propeller at a comparatively low pitch which permits quick lifting of the plane, and after the plane has been lifted the speed of the motor is reduced and the angularity of the blades is automatically changed to one in which a greater grip of the blades is obtained on the air for the purpose of obtaining the maximum propelling effect of the propeller.

As a result of this the aeroplane will be lifted from the ground positively and promptly and with greater ease and smoothness of action than has been possible heretofore by a relatively high speed of the engine and then propelled in the air at a high speed while the speed of the engine is reduced, thereby insuring better control of the aeroplane and greater safety in its operation. From the foregoing explanation it will now be clear that the supporting ring 34 engages with the outwardly facing shoulder 37 on the radial guide tube 13, and this supporting ring is .itself provided with another internal outwardly facing shoulder 35 on which a ball bearing is seated and provides means in which the shank 15 of the propeller blade slides and turns, this ball bearing being engaged by a cap which is connected with said tube for holding the bearing in place.

The mechanism whereby this is accomplished is comparatively simple and compact in construction, and its several parts are so organized that the same are not liable to be injured or get out of order, and they are also readily accessible for inspection, adjustment and repairing.

I claim as my invention:

1. An automatic variable pitch propeller comprising a hub adapted to be mounted on a rotating driving member and having a radial guide tube, a propeller blade having a radial shank movable lengthwise in said tube, said tube provided at its outer end with an outwardly facing shoulder and in its side with a helical slot, a supporting ring engaging said shoulder and itself provided with another internal outwardly facing shoulder. a

ball bearing which is seated on the shoulder of said ring and in which said shank slides and turns, a cap engaging said ball bearing and connected with said tube, a collar secured to the inner end of said shank, aspring interposed between said collar and suporting ring, and a pin projecting laterally from said collar and engaging with said helical slot.

2. An automatic variable pitch propeller comprising a hub adapted to be mounted on a rotating driving member and having a radial guide tube, a propeller blade having a radial shank movable lengthwise in said tube, said tube provided at-its outer end with an outwardly facing shoulder and in its side with a helical slot, a supporting ring engaging said shoulder and itself provided with another internal outwardly facing shoulder, a ball bearing which is seated on the shoulder of said ring, and in which said shank slides and turns, a cap engaging said ball bearing and connected with said tube, a flat sided neck at the inner end of said shank, a collar having a fiat sided bore engaging said neck, a pin projecting from said collar into said slot, and. a spring interposed between said collar and ring.

3. An automatic variable pitch propeller comprising a hub adapted to be mounted on a rotating driving member and having a radial guide tube, a propeller blade having a radial shank movable lengthwise in said tube, said tube provided at its outer end with an outwardly facing shoulder and in its side with a helical slot, a supporting ring engaging said shoulder and itself provided with another internal outwardly facing shoulder, a ball hearing which is seated on the shoulder of said ring, and in which said shank slides and turns, a cap engaging said ball bearing and connected with said tube, a collar secured to the inner end of said shank, a spring interposed between said collar and supporting ring, a pin projecting laterally from said collar and engaging with said helical slot, and a packing mounted on said cap and surrounding said shank.

ROBERT L. KELM. 

